Shared Azure middleware between Azure Monitor and Prometheus datasources (#46002)

* Scopes in Azure middleware

* Enable Azure middleware without feature flag

* Use common Azure middleware in Azure Monitor

* Apply feature flag to JsonData configuration of Azure auth

* Enforce feature flag in Prometheus datasource

* Prometheus provider tests

* Datasource service tests

* Fix http client provider tests

* Pass sdkhttpclient.Options by reference

* Add middleware to httpclient.Options

* Remove dependency on Grafana settings

* Unit-tests updated

* Fix ds_proxy_test

* Fix service_test

pkg/plugins/config.go

@@ -2,6 +2,7 @@ package plugins
 
 import (
 	"github.com/grafana/grafana/pkg/setting"
+	"github.com/grafana/grafana/pkg/tsdb/azuremonitor/azsettings"
 )
 
 type Cfg struct {
@@ -19,7 +20,7 @@ type Cfg struct {
 	AWSAssumeRoleEnabled    bool
 
 	// Azure Cloud settings
-	Azure setting.AzureSettings
+	Azure *azsettings.AzureSettings
 
 	BuildVersion string // TODO Remove
 }